8090Al—Li合金的疲劳裂纹扩展

研究了8090型Al—Li合?疲劳裂纹扩展行为以及组织结构和环境的影响,结果表明,在空气中,自然时效和欠时效?现出最好的疲劳裂纹扩展阻力,其次是峰时效状态,而过时效状态的疲劳裂纹扩展阻力最低,在3.5%NaCl水溶液中,时效状态对疲劳裂纹扩展行为有着同空气中相同的影响规律,但在同样的时效条件下,在3.5%NaCl水溶液中的疲劳裂纹扩展阻力要比空气中的低,在相同的应力强度因子范围△K作用下,缺口短裂纹和物理短裂纹均表现出比长裂纹高的扩展速率,用位错的平面滑移性和循环滑移可逆性解释了时效的影响,用裂纹的闭合效应和裂纹尖端塑性区尺寸说明了长短裂纹扩展行为的差别。

FATIGUE CRACK PROPAGATION IN Al-Li ALLOY 8090

Fatigue crack growth rates of 8090 type Al-Li alloy in air were found to be strongly dependent upon the aging conditions. The naturally aged and underaged specimens showed the highest resistance to the fatigue crack propagation. The fatigue crack growth re- sistance of the overaged specimen is the lowest and that of the peakaged specimen in between. As compared to air, 3.5%NaCl solution did not change the effect of aging conditions on the fatigue crack growth, but caused a decrease of the resistance to the fatigue crack growth un- der the same aging condition. Both short cracks from notch and physically short cracks showed much higher rates of fatigue crack propagation in comparison with long cracks under the same aging condition and stress intensity level. The growth behavior of the short crack depends on its type. The growth rate of short crack from notch decreases first to a minimum and then increases with increasing AK. However, the physically short crack grows at a progressively increasing rate. The effects of aging conditions were explained in terms of the slip planarity of dislocations and the cyclic slip reversibility. The observed short crack behav- ior was considered to be dependent on the crack closure and the local plasticity near the crack